This study has two major objectives. The first is to determine neurophysiologically which of the many carotid body preparations is the best one to use in studies of carotid body chemoreceptor function. The second is to apply the optimal preparation to determine the role of the chemoreceptors in mediating ventilatory acclimatization to chronic hypoxia. We shall attempt to provide answers to the following questions in striving to attain our goals. 1) Are there differences among the results obtained relative to chemoreceptor function that are attributable to differences in the preparations from which they were obtained? 2) Does chronic hypoxia change the sensitivity of carotid body chemoreceptors to hypoxia? 3) Can changes in the levels of brain extracellular fluid pH affect chemoreceptor function? 4) Does dopamine play a role in mediating ventilatory acclimatization to chronic hypoxia? We shall attempt to develop a completely innervated carotid body preparation for the neurophysiological studies necessary to answer the first three questions. The analysis of carotid body dopamine will employ biochemical assays utilizing high performance liquid chromatography using strong cation exchange resin coupled with an electrochemical detector.